HIV infection involves the interaction of the virus and its host. It is likely that viral infection results in the modulation of the expression of some cellular genes. The identification of these genes may be important for understanding the infection process and to provide clues to strategies for antiviral therapy. For example, abnormal expression of a surface protein may provide a marker that could be used to target infected cells with antibody-conjugated toxins. We have used the subtractive hybridization method to try to identify differentially-expressed genes in HIV-infected and uninfected macrophages. Many clones have been isolated and most have failed to be differential by Northern analysis. There are two clones still being characterized. Using the same RNA from HIV-infected and uninfected macrophage, kindly provided by Howard Gendelman, we are pursuing a differential display technique (Liang and Pardee, Science 1992;257:967-71). The mRNA is reverse transcribed with oligo dT primers and then a PCR is carried out with the oligo dT primer and random 10-mer. Primers are selected to display an optimal number of amplified fragments on the sequencing gel and represent the mRNA. A band in one lane and not the other indicates a dissimilarity or unique gene. We have currently identified many differences and are presently isolating these bands for probing Northerns (RNA gel blots) and screening cDNA libraries.